1. Field of the Invention
The present invention generally relates to plasma enhanced semiconductor wafer processing chambers. More specifically, the invention relates to the method and apparatus for routing harmonics in a plasma to ground within a plasma enhanced semiconductor wafer processing chamber.
2. Description of the Related Art
A plasma enhanced semiconductor wafer processing reactor generally comprises a vacuum vessel for containing one or more gases, a pedestal for supporting a semiconductor wafer or other workpiece within the vacuum vessel, and a power supply for applying energy to the gases to form a plasma within the vacuum vessel. Depending upon the structure of the vessel and the nature of the gases, processing within the vessel may include physical vapor deposition, chemical vapor deposition, plasma annealing or etching. In some chambers, particularly, a reactive ion etch chamber, the radio frequency (RF) power may be applied to the pedestal that supports the wafer, while the vessel itself is grounded. The RF power couples to the gases in the vessel and ignites a plasma.
During plasma processing, the plasma sheath proximate the pedestal forms a non-linear rectifier that produces harmonic energy within the plasma. The harmonic energy is at frequencies that are harmonics of the frequency of the applied RF power. Such harmonics distort the operation of the plasma and can cause nonuniformity in the plasma processing of the wafer. Such nonuniformities manifest themselves in an etch reactor as a nonuniform etching of the wafer and manifest themselves as non-uniform deposition in a deposition chamber. Nonuniform etching of a wafer can cause ineffective etching of certain portions of the wafer, as well as induce currents in the devices that have been formed on the wafer and destroy those devices.
Therefore, there is a need in the art for a method and apparatus for controlling harmonics that are generated in the plasma.